1. Field of the Invention
This invention generally relates to a linear motion rolling-contact bearing assembly including a rail, a slider and a plurality of rolling members interposed between the rail and the slider to provide a rolling contact therebetween, and in particular to an endless linear motion roller bearing assembly including an endless circulation path defined between the rail and the slider for rollers which provide a rolling contact therebetween.
2. Description of the Prior Art
An endless linear motion rolling contact bearing assembly is well known in the art and, in general, it includes a rail, a slider, a plurality of endless circulation paths defined between the rail and the slider and a plurality of rolling members provided in the plurality of endless circulation paths for providing a rolling contact between the rail and the slider to thereby provide a relative linear motion between the slider and the rail. The rolling members may be either balls or rollers depending on applications. Each endless circulation path for the rolling members includes a load path section, a return path section and a pair of connecting path sections each connecting the corresponding ends of the load and return path sections. The load and return path sections are typically straight and the pair of connecting path sections are curved, typically semicircular. Since the endless circulation path defines an endless loop, the rolling members provided in the endless circulation path may roll indefinitely to thereby provide theoretically an indefinite length of a relative motion between the rail and the slider.
As the operating speed of an endless linear motion rolling contact bearing assembly increases, the centrifugal force acting in each of the rolling members as it rolls along the curved connecting path section increases and thus the rolling members tend to become more pressed against the outer wall surface of the curved connecting path section. As a result, a component of the slider which defines the curved connecting path section is required to have a wear resistant characteristic and a high rigidity. In order to provide a high mechanical strength, the prior art slider was typically formed from a steel material. However, this produced a disadvantage of increasing the overall weight of the slider, thereby impairing the high-speed operation. In order to cope with this situation, there was proposed to form the slider from a synthetic resin material and to provide a guide member of a thin steel plate at the deepest portion of the curved connecting path section integrally with the synthetic resin slider for an endless linear motion ball bearing assembly employing balls as the rolling members as disclosed in the Japanese Utility Model Application No. 56-51825 (Utility Model Laid-open Publication No. 60-17540) assigned to the assignee of this application.
However, it has been found that the structure described in the above-identified application still suffers from wear and the operating speed is rather limited. In particular, since the structure described in the above-identified application was proposed for an endless linear motion ball bearing assembly using balls as rolling members, there still remained a difficulty for other types of an endless linear motion rolling contact bearing assemblies, such as the one using rollers as rolling members.